This invention relates to a liquid feed pump particularly used in an apparatus for filling an ampule or the like with liquid medicine and a liquid feed apparatus utilizing such liquid feed pump to perform such operation of liquid medicine filling.
Most commonly a pump of the piston type, made of metal and glass, has been used for filling of liquid medicine. Though not extensively, a diaphragm pump made of synthetic resin also has been used as simplified filling equipment.
Additionally, a pump of piston type adapted for CIP (Clean In Place) and SIP (Sterile In Place) is also commercially available. The pump of the piston type is disadvantageous in that a slidable movement of the piston with respect to the cylinder is apt to generate particles. Presence of the parts which are slidably movable often results in deteriorating the surface of the pump chamber destined to be exposed to the liquid medicine and makes it impossible to achieve a satisfactory washing effect unless the pump is dismantled and subjected to ultrasonic washing or the like.
Such problem encountered by the pump of the piston type can be solved by the diaphragm pump which includes no slidably movable part. The diaphragm pump is well known in which the metallic diaphragm provided within the pump chamber is reciprocated so as to change a volume of the pump chamber and thereby the quantity of liquid that has been sucked through the liquid inlet into the pump chamber and is discharged through the liquid outlet.
A. Japanese patent application Disclosure Gazette No. 1979-108003 discloses a pumping apparatus for proportional control of a micro flow rate so arranged that a metallic diaphragm magnetically attracted by an iron core under an exciting effect of a solenoid coil bears against an O-ring secured to the upper end of the iron core. In this pump well known to the art, the metallic diaphragm is reciprocated with a predetermined stroke and a frequency of electric signals may be changed to change a repetition rate at which the metallic diaphragm is reciprocated and thereby to change a flow rate of the fluid.
B. Japanese patent application Disclosure Gazette No. 1988-176679 discloses a piezo-electric pump utilizing a laminated piezo-electric element to drive the diaphragm so as to achieve suction and discharge of fluid.
However, these conventional pumps utilizing the metallic diaphragms are inconvenient in that the desired liquid feed can be achieved only at a small flow rate since the diaphragms used in these pumps disadvantageously have small strokes.
More specifically, the above-mentioned pumping apparatus A is constructed so that the metallic diaphragm is magnetically attracted by the iron core under the exciting effect of the solenoid coil and, when the solenoid coil is not energized, a movable plate pushes the metallic diaphragm upward under a force of a spring and thereby changes a volume of the pump chamber. The invention of this Disclosure Gazette leaves unsolved a problem that a desired large stroke cannot be obtained only by the magnetic attraction of the metallic diaphragm under the exciting effect since the metallic diaphragm inherently has a high rigidity.
In addition, the invention of this Disclosure Gazette wherein a metallic diaphragm magnetically attracted under an exciting effect bears against an O-ring, leaves another problem unsolved such that the stroke is not stabilized and therefore it is difficult to maintain a quantity of liquid to be fed at a constant level since the O-ring against which the metallic diaphragm bears upon excitation of the solenoid coil is made of elastic material such as synthetic resin or rubber.
The above-mentioned piezo-electric pump B is also disadvantageous in that the length of the stroke is severely restricted and it is impossible to assure a constant quantity of liquid to be fed since the stroke relies upon expansion and contraction of a laminated piezo-electric element which is applied with voltage.
As far as washing and sterilization are concerned, the pump of a metallic diaphragm making CIP as well as SIP possible is preferred as the liquid feed means, particularly for liquid medicine, to that of the pump of the piston type which can neither be washed nor sterilized without dismantling the pump. However, it is difficult for the conventional metallic diaphragms as employed in the above-mentioned prior art to assure a constant quantity of liquid to be fed and the pump employing such metallic diaphragm, well known to the art, cannot satisfactorily function as the liquid feed means particularly for filling of liquid medicine. It should be also understood that various containers such as an ampule and a vial cannot be accurately filled with liquid medicine merely by employing the liquid feed pump of the diaphragm type since dripping of the liquid medicine out of the filling needle occurring before and after filling cannot be avoided.